1. Field of the Invention
The present invention relates to an organic light emitting display device, and more particularly, to an organic light emitting display device that is capable of preventing the permeation of moisture by changing a sealing structure and a material, thereby preventing the degradation of pixels and thus improving look-and-feel characteristics and a method of manufacturing the same.
2. Discussion of the Related Art
An organic light emitting display device, one of the flat panel displays, is a self-luminous type display device. Consequently, the organic light emitting display device has a higher contrast than a liquid crystal display. Also, the organic light emitting display device does not need a backlight, and therefore, it is possible to reduce the size and weight of the organic light emitting display device. Furthermore, the organic light emitting display device has low power consumption.
In addition, the organic light emitting display device is driven by direct current having low voltage, the response speed of the organic light emitting display device is high, and components of the organic light emitting display device are all solid. Consequently, the organic light emitting display device is strong to external impact, and the organic light emitting display device has a wide temperature range. In particular, it is possible to manufacture the organic light emitting display device at low costs. Furthermore, only deposition and encapsulation equipment is needed to perform a process of manufacturing the organic light emitting display device, unlike when manufacturing a liquid crystal display or a plasma display panel (PDP) Consequently, a process for manufacturing the organic light emitting display device is very simple.
Also, when the organic light emitting display device is driven in an active matrix type structure having a thin film transistor, which is a switching element, for each pixel, the organic light emitting display device exhibits the same brightness although low current is supplied to the organic light emitting display device. Consequently, the organic light emitting display device has advantages in that the power consumption of the organic light emitting display device is low, high resolution of the organic light emitting display device is achieved, and it is possible to greatly increase the size of the organic light emitting display device.
The organic light emitting display device excites a fluorescent material using carriers such as electrons and holes to display video images.
Meanwhile, the organic light emitting display device is principally driven in a passive matrix type structure having no thin film transistor.
However, the passive matrix type structure is under many restrictions relating to resolution, power consumption, and service life. For this reason, research and development have been carried out on an active matrix type organic light emitting display device necessary to manufacture a new-generation display requiring high resolution and a large-sized screen.
Also, depending upon where a light emitting layer is located on upper and lower substrates, the organic light emitting display device may be classified as a lower light emitting type organic light emitting display device or an upper light emitting type organic light emitting display device. When the upper light emitting type organic light emitting display device is implemented in the active matrix type structure, a thin film transistor array is disposed on the lower substrate, and the light emitting layer is located on the upper substrate, which is called a dual plate type organic light emitting display device (DOD).
Hereinafter, a conventional organic light emitting display device will be described with the accompanying drawings.
FIG. 1 is a sectional view schematically illustrating a sealing structure of a conventional organic light emitting display device, and FIGS. 2A and 2B are photographs respectively illustrating initial normal pixels and pixels degraded by a hygroscopic phenomenon of the conventional organic light emitting display device.
As shown in FIG. 1, conventional organic light emitting display device includes a first substrate 10 having a display region defined in the middle thereof and a non-display region defined at the edge thereof, and a second substrate 20 having a display region defined in the middle thereof and a non-display region defined at the edge thereof, the first substrate 10 and the second substrate 20 being opposite to each other, and a seal pattern 30 formed by bonding the first substrate 10 and the second substrate 20 at the non-display regions between the first substrate 10 and the second substrate 20.
At the display region defined inside the seal pattern 30 are provided a plurality of pixels which emit light according to the principle of an organic light emitting diode.
Also, the seal pattern 30 is cured by irradiating ultraviolet rays to the lower side of the first substrate 10 or the second substrate 20 after bonding the first substrate 10 and the second substrate 20. At this time, the ultraviolet curing seal pattern 30 may be degraded by moisture due to the properties of a material for the seal pattern. For this reason, the improvement to the material for the seal pattern is required. Also, a hygroscopic agent may be applied to the inside of the substrate in order to prevent the permeation of external moisture or gas. In this case, however, the thickness of the device is increased. Furthermore, the use of the hygroscopic agent is limited to fundamentally prevent the permeation of moisture.
The ultraviolet curing seal pattern 30 has the following problems.
Specifically, the seal pattern 30 is an organic material curable by ultraviolet (UV) rays. Due to the properties of the organic material, moisture may easily permeate through the seal pattern 30, and the seal pattern 30 may be easily separated from the surface of the first substrate 10 or the second substrate 20. Consequently, when the seal pattern 30 is separated from the surface of the first substrate 10 or the second substrate 20, or when moisture (H2O), carbon dioxide (CO2) or hydrogen (H2) permeates through the seal pattern 30, pixels located in the display region inside the seal pattern 30 are gradually degraded from the edge toward the middle thereof, with the result that the pixels are deformed from the normal shapes of FIG. 2A to the abnormal shapes of FIG. 2B, and therefore, the regions that can be driven as the normal pixel regions shrink. Also, the hygroscopic phenomenon becomes more serious with the passage of time, and the shrinkage phenomenon of the respective pixels located inside the seal pattern 30 becomes more serious. As a result, the service life of the organic light emitting display device under the hygroscopic phenomenon decreases.
The above-described conventional organic light emitting display device has the following problems.
The conventional seal pattern, used to seal between the opposite first and second substrates, is an ultraviolet curing type organic seal pattern. The seal pattern is cured by irradiating ultraviolet rays to the lower side of the first substrate or the second substrate. The ultraviolet curing type organic seal pattern has problems in that moisture or the like may easily permeate into the seal pattern according to external environment, and the seal pattern may be easily separated from the substrates, which are made of glass, whereby external gases are introduced into the display region to degrade the organic light emitting layer from the edge of the organic light emitting layer, with the result that the size of the pixels decreases. There are many restrictions in solving such degradation problem, and therefore, there is a high necessity to improve a material for the seal pattern.